The present invention relates to articles that employ shape-memory alloy which exhibits the shape-memory effect as a motive mechanism when exposed to a pressure wave, as well as to thermal enhancement means to improve and/or control the speed of recovery of the shape-memory alloy, i.e., to initiate the shape-memory effect.
Articles can be adapted to a variety of uses wherein the basic theory of impact mechanics is applicable. Naturally, the theory is easiest to explain using projectiles as examples. Other applications deal with one or more axis acceleration detectors which are useful in vehicles or stationary objects experiencing shock.
Using projectiles as an example, and with improving the impact energy transfer efficiency of projectiles being the goal, the following description provides a background of the invention.
Projectiles in the form of conventional bullets remain intact upon striking a soft target to cause a single wound tract. While conventional bullets may expand or tumble after impacting the soft target in order to increase the lethality of the bullet, the bullet will frequently start its expanding or tumbling action only after much of the target has been penetrated. Prior art methods for improving impact energy transfer efficiency, and thus bullet lethality, generally involve alteration of the external configuration of the bullet to the shapes of "hollow-point", "off-center punch", "spoon nose" and the like.
U.S. Pat. Nos. 3,173,371; 3,861,314 and 4,338,862 disclose various attempts to alter the performance of a projectile by altering its external configuration to promote instability upon impact, or by altering the internal configuration of the projectile through the use of passive elements such as a disc or a low-density filler material. None of the prior art devices discloses a projectile having an active means to improve and/or control the impact energy transfer efficiency of the projectile. By the word "active" it is meant that the means has stored energy which will act as a motive mechanism. The prior art devices are "passive" in that the elements of their structure are moved only by external forces.
Acceleration detectors likewise depend upon passive elements which are moved by external forces. None of these detectors is known to have a positive means to improve the sensing ability of the detectors. Such a positive means would be useful in a myriad of devices in sensing not only acceleration, per se, but also in sensing its application to impact, shock and pressure waves.